1. Field of the Invention
The present invention relates generally to a security system for detecting a cut telephone line, and more particularly is concerned with a circuit for activating an alarm when a telephone service line is cut and transmitting a signal over a telephone trunk line.
2. Description of the Prior Art
Many security systems have been developed for detecting an unauthorized entrance. A common system utilizes sensors to detect vibrations at entry points, smoke, etc. When activated, the sensors send a signal to a central processing unit which in turn activates an alarm, switches on floodlights, etc. Oftentimes, the central processing unit includes a dialer which sends a taped message over telephone lines to authorities such as police, fire, medical services, etc.
Such systems are vulnerable to cut telephone lines. Once a telephone line is cut, the system can no longer dial a selected number. Intruders can proceed with the knowledge that the detection system can not dial for assistance.
Many telephone monitoring systems require continuous monitoring of a line. Other systems can not send a signal or call once a line is cut, or require a second line to send a call. For example, a telephone monitoring system, Versus 90, is sold by Base Ten Systems, Inc. of One Electronics Drive, Trenton, N.J. 08619. The device uses existing telephone connections and can be tied to a variety of detection sensors. When activated, a signal is sent over telephone lines to a monitoring agency. The agency in turn receives the signal and notifies the proper authorities. The system sends a continuous inaudible electronic signal every half second. If the telephone line is cut, the interruption can be detected immediately. U.S. Pat. No. 4,529,971 issued to James in 1985 and assigned to Base Ten Systems, Inc. discloses an apparatus for indicating a break in lines leading from a base station to a monitored instrumentality.
An AC Power/Telephone Line Monitor is sold by ADEMCO, 165 Eileen Way, Syosset, N.Y. 11791. The device monitors the incoming telephone line to a digital communicator or tape dialer and the AC input to a control panel. If a telephone line fault occurs, a local alarm will be activated and a communicator will call out on a second telephone line.
U.S. Pat. No. 3,852,541 issued to Altenberger in 1974 discloses a burglar alarm actuated by cutting of a telephone wire. An alarm relay switch-actuating circuit is connected to telephone wire contacts. A full-wave bridge rectifier prevents erroneous matching of polarity to the circuit. When a telephone line is cut, a relay switch closes to actuate an alarm. However, the circuit does not provide a system for alerting a phone company that a line has been cut.
U.S. Pat. No. 4,258,357 issued to Browell in 1981 discloses an alarm signaling system which is monitored by a telephone company. When the signaling condition is removed from a telephone line by, for example, a burglar detection system, equipment at the telephone company activates an alarm. Whenever the telephone line is cut, the alarm is tripped.
U.S. Pat. No. 3,919,705 issued to Stendig et al. in 1975 discloses a loop cord alarm system for preventing unauthorized removal of plugs for electrical appliances. When a plug is removed, a relay is deenergized, actuating contacts to generate an alarm.
Consequently, a need exists for improvements in telephone monitoring systems. A system should activate an alarm once a line is cut without continuous monitoring of the telephone line. It is desirable that a system send a signal over the telephone to notify the telephone company that a service line has been cut.